Type 1 or Insulin-Dependent Diabetes Mellitus (IDDM) arises in genetically predisposed individuals as a consequence of immune-mediated destruction of the pancreative islet insulin secreting beta-cells. It is possible to identify impending clinical IDDM through the detection of antibodies directed against self-antigens of the pancreatic beta- cells. First degree relatives of individuals with IDDM have more than ten-fold the risk of IDDM than the general population. Initial blood (serum) screening will be for islet cell autoantibodies (ICA). Those individuals found to have ICA will then be staged into one of four different categories of risk of developing IDDM, dependent upon their point of progression to the clinical disease. IDDM risk assessment in non-diabetic relatives is based upon a number of factors, including: genetic susceptability, age, the presence of ICA especially if found together with insulin autoantibodies (IAA), and the degree of loss of first phase (1+3 minute) plasma insulin response (FPIR) during an intravenous glucose tolerance test (IVGTT). "High risk" relatives will be those that have been predicted to have at least a 50% probability of developing IDDM within the next five years on the basis of positive ICA and low FPIR to IVGTT. "Moderate risk" relatives are those with positive ICA, but normal FPIR to IVGTT. This group if further divisable into those with an intermediate risk on account of positive IAA and those with a "modest risk" who are ICA negative. The "low risk" relatives lack ICA. In the "high risk" group, the protocol is designed to determine whether parenteral insulin therapy, consisting of periodic courses of continuous intravenous insulin, with accompanying chronic subcutaneous insulin, will delay their expectant development of clinical IDDM. The trial is a randomized, controlled, multicenter clinical trial, in which subjects randomized to an EXPERIMENTAL GROUP will have the active intervention, while subjects randomized to the STANDARD GROUP will be closely monitored and offered treatment at the earliest signs of IDDM. The intervention protocol for the "intermediate risk" group is designed to determine whether presentation of an islet cell autoantigen (i.e. orally ingested insulin) to the immune system via the intestinal mucosa could induce disease relevant immunological tolerance, thereby delaying the development of IDDM.